1. Field of the Invention
The present invention relates to a frequency synthesizing apparatus for a radio frequency (RF) transceiver, and more particularly, to a frequency synthesizing apparatus and method which can reduce a circuit area and may be low powered, and also can reduce signal distortion.
2. Description of Related Art
A frequency synthesizer generating a local oscillation (LO) signal or an LO generation block is required in a system for transmitting/receiving wireless data, such as a mobile phone, a digital multimedia broadcasting (DMB) phone, and a personal digital assistant (PDA). In this instance, an LO signal is required in a mixer of a transceiver to up/down-convert a frequency of a transmitted/received signal. As an example, a frequency synthesizer is utilized to down-convert a received RF signal into a baseband signal or to up-convert a baseband signal into a carrier signal, in a Code Division Multiple Access (CDMA) system, a global positioning system (GPS), a personal communication system (PCS), an International Mobile Telecommunication (IMT) 2000 system, Wireless Broadband Internet (WiBro) system, a wireless local area network (WLAN) system, an Ultra Wideband (UWB) system, and a WiMax system for a ubiquitous system.
FIG. 1 is a diagram illustrating a related frequency synthesizer 100 generating two high frequency signals having a different phase from each other. Referring to FIG. 1, the frequency synthesizer 100 includes two single side band (SSB) mixers 110 and 120, a selector 130 and a buffer 140.
Each of the two SSB mixers 110 and 120 receives a first high frequency signal RF1I and a second high frequency signal RF2I and quadrature-phase (Q) signals thereof, RF1Q and RF2Q. Also, each of the two SSB mixers 110 and 120 generates an SSB signal RFOI/RFOQ, whose frequency is an addition of frequencies of the two received signals or a difference therebetween, and which have a 90 degree phase difference from each other. In this instance, a Q signal is a signal having a 90 degree phase difference from an in-phase (I) signal.
The selector 130 selects and outputs the SSB signals RFOI and RFOQ, another high frequency signals RFXI and RFXQ that have a 90 degree phase difference from each other, or yet another high frequency signals RFYI and RFYQ that have a 90 degree phase difference from each other. Depending on an RF system, the high frequency signals RFXI and RFXQ may be the first high frequency signal RF1I and the Q signal thereof, RF IQ, and the high frequency signals RFYI and RFYQ may be the second high frequency signal RF2I and the Q signal RF2Q thereof. Also, other signals having other frequencies that are generated in other mixers, a phase-locked loop (PLL) or a voltage-controlled oscillator (VCO) may be input as the high frequency signals RFXI and RFXQ or the high frequency signals RFYI and RFYQ.
In addition to the SSB mixers 110 and 120, and the selector 130 shown in FIG. 1, a plurality of other SSB mixers and selectors may be utilized for processing a multi-band in a ubiquitous system.
An I signal and a Q signal thereof selected in the selector 130 are generally processed in the buffer 140 and input into a receiver (Rx) mixer or a transmitter (Tx) mixer of an RF transceiver. In this instance, the buffer 140 is a circuit element in the structure of a differential amplifier or an inverter. Also, the buffer 140 sufficiently amplifies an I signal and a Q signal thereof output from the selector 130, or increases a driving power thereof.
As described above, necessary multi-band signals may be generated using a large number of SSB mixers. However, in this case, a required circuit area may be unacceptably increased to accommodate a PLL, a VCO and SSB mixers, and a large amount of power may also be consumed. Also, since a large number of circuits are utilized, the distortion or offset of a signal is increased which makes it difficult to generate a stable signal.